This invention relates generally to devices and methods for trapping blood clots and controlling embolization and some of the complications of thrombosis in blood vessels. More particularly, this invention relates to a blood filtering system that comprises two separable independent parts: a permanent anchor, and a filter removably attached to the anchor. The two parts of the system are attached in such a way that, once emplaced, the filter is continuously maintained along the central axis of the blood vessel to ensure that the filter operates at optimal efficiency. If and when it is necessary or desirable to remove the filter, it may readily be separated from the anchor and withdrawn, leaving a permanently attached anchor that does not interfere with blood flow within the blood vessel.
The presence of thrombus within the body""s circulatory system presents significant health hazards, as manifested by potential acute venous thrombosis and chronic deep vein thrombosis. Acute venous thrombosis can lead to pulmonary emboli, a potentially lethal condition when an embolus travels into the pulmonary arteries. Currently, the most widespread treatment is the administration of systemic and oral anticoagulants such as heparin and coumadin, and thrombolytic agents such as TPA, urokinase and streptokinase.
Unfortunately, conventional drug therapy is ineffective or inappropriate for controlling emboli within the circulatory system of some patients. In particular, since most pulmonary emboli originate in veins of the lower limbs, pelvis or inferior vena cava, it has been recognized that life-threatening pulmonary emboli can be prevented from reaching the lungs by mechanically interrupting the inferior vena cava to filter out emboli.
Indications for introducing such filters in the inferior vena cava include:
a) Pulmonary embolism in patients with a high risk of internal bleeding, including those having surgery, anticipated surgery, recent trauma, cerebral hemorrhage or peptic ulcer disease who are not amenable to anticoagulant or thrombolytic therapy.
b) Recurrent pulmonary emboli notwithstanding anticoagulant therapy.
c) Patients showing large free-floating thrombi in the iliofemoral veins or inferior vena cava as identified with venography.
d) As prophylaxis against pulmonary emboli in older patients with high-risk conditions.
e) Disseminated thrombosis and profound thrombo-cytopenia in patients displaying heparin sensitivity.
f) Prevention of recurrent pulmonary emboli after pulmonary thrombolectomy.
In 1967-68, Eichelter and Schenk described an umbrella-like device which they introduced under local anesthesia into the femoral vein of dogs to filter emboli. Eichelter P. Schenk, W. G., Jr.: xe2x80x9cA New Experimental Approach to Prophylaxis of Pulmonary Embolismxe2x80x9d. rev Surg 24:455-456 (Nov.-Dec.) 1967; Eichelter P. Schenk, W. G. Jr.: xe2x80x9cProphylaxis of Pulmonary Embolism.xe2x80x9d Arch Surg 97: 348-356 Aug. 1968. The Eichelter/Schenk device was constructed by making longtitudinal incisions circumferentially around a segment of a polyethylene tube, placing a tube of smaller diameter inside the larger tube and flaring the end protruding beyond the linear incisions. Light traction of the inner tube while holding the outer tube stable produced an umbrella-like structure. Unfortunately, this structure included numerous apertures for trapping stagnant blood and thereby promoting highly undesirable thrombosis and potential embolization.
Eichelter and Schenk made small incisions in the right femoral veins of the groins of the dogs used in the tests with the distal portion of the catheter tied into the femoral vein and the device open at a point lying distally to the renal veins. After a number of weeks, the device was collapsed and removed through a small incision. The embolization of trapped or attached emboli upon removal of the Eichelter/Schenk device precluded use of this device in humans.
A permanent implantable vena cava filter was developed by Mobin-Uddin in 1969, and described in U.S. Pat. No. 4,540,431. This filter was intended to be introduced through an incision in the jugular vein. The Mobin-Uddin filter was an umbrella-like structure having expanding ribs carrying sharpened points at their divergent ends which impaled the wall of the blood vessel when the filter was positioned at the desired location and permitted to expand into its operative structure. The Mobin-Uddin filter had a high occlusion rate and therefore was not widely used. Finally, even if initially properly implanted, these filters could come loose and migrate to either ineffective or dangerous and life-threatening locations in the vascular system.
The present invention solves the problems inherent in the prior art devices by providing a system establishing a quick, safe, and well-centered reliable emplacement of an effective emboli filter which is secure in the vessel until it becomes desirable or necessary to remove the filter. The present invention is particularly useful for placement in the inferior vena cava. The system may also be useful in filtering clots in other areas of the vascular anatomy.
It is therefore an object of the present invention to provide a two stage blood clot filtering system which can be quickly and safely emplaced within a blood vessel to efficiently trap emboli passing through the vessel.
Yet another object of the present invention is to provide an emplacable blood clot filtering system which, while maintaining patency, can provide either permanent or temporary protection from emboli in blood vessels.
It is yet another object of the present invention to provide a blood clot filtering system which can be emplaced through the femoral or internal jugular vein in a relatively simple procedure, during the course of which the system may be readily repositioned until optimally located in the vessel, and then positively fixed in that location for the desired, medically appropriate period.
A further object of the present invention is to provide a blood clot filtering system which can be steered through the vena cava under appropriate imaging techniques.
A still further object of the present invention is to provide an emboli or blood clot filter which, once emplaced, remains suspended along the longitudinal axis of the vessel as blood flows through the filter, minimizing endothelialization and vessel wall contact on the removable portion.
Another object of the present invention is to provide an emboli filter for emplacement in a blood vessel which can be permanently emplaced but which also can be readily removed when desired.
Yet another object of the present invention is to provide a blood clot filtering system for emplacement in blood vessels in which the patency is optimized and release of emboli into the bloodstream upon removal of the filter from the vessel is minimized.
Still another object of the present invention is to provide a blood clot filtering system including an anchor that is permanently emplacable in a blood vessel, and a removable filter attached to the anchor, in which endothelialization of the filter is minimized.
The present invention is therefore directed to a blood clot filtering system including an anchor which is permanently emplacable in a blood vessel and a blood clot filter removably attached to the anchor.
The anchor is radially self-expanding. It may be made of a metal spring wire material bent into a close zig-zag formation, with alternating zig and zag legs meeting at sharp angles at their distal and proximal vertices. At least two hooks may be provided respectively at least two distal vertices spaced equidistantly on a circle defined by the distal vertices.
The filter preferably includes two stages which cooperate to provide enhanced clot catching. The first stage comprises a series of distally projecting legs evenly spaced about the longitudinal axis of the filter, and the second stage comprises a series of generally radially projecting legs also evenly spaced about the longitudinal axis of the filter. The first stage may be also provided with a series of flexible filamentous tethers. The filter is removably attached to the anchor by way of these tethers. Finally, the filter may include a spring-loaded jaw at its proximal end. This jaw will retain both ends of each of the tethers when the tethers are attached to the anchor, but will release one end of each of the tethers in the process of removing the filter, leaving the anchor permanently fixed in place.